The nodes include indexed hexagonal UVs, which are very useful for various effects. This way you can address each cell individually.

Simple Hex - for basic hexagon patterns
Distorted Hex - for complex organic hexagon patterns with distortion and noise per cell already set up
Simple Hex Rounded - similar to "simple hex" but with adjustable rounded corners
Distorted Hex Rounded - similr to "distorted hex" but with adjustable rounded corners

Also included are 7 basic shaders with simple explanation/documentation and 6 complex shaders (some animated) to show you what is possible.

Added a rounded-hex node to the file, so you can have a hexagon texture with adjustable rounded corners.

Optimized the overall node layout
Integrated the rounded hexagon texture into two new nodegroups.
Created a additional cobblestone shader to show the possibilities with the rounded hex node.
Created a new file (example_cobblestone.blend) to show what is possible with the cycles renderer and geometry displacement.
Added optimized versions for blender 2.81.